Terrestrial pulmonate gastropods such as slugs and snails are significant plant pests that affect commercial agriculture and horticulture and domestic gardens. These organisms are omnivorous and consume large amounts of vegetative material during their daily foraging. Consequently, they can seriously damage vegetable gardens and even plant crops during all phases of the growing cycle. Because of their destructive potential, control measures must be used to ensure adequate protection of the growing plants.
Aquatic molluscs, including the fresh water snails, Golden Apple Snail, Pomacea canaliculata, Bulinsu sp., Bulinus, Biomphalaria, and Oncomeania, and vectors of parasitic worms (e.g., Schistosoma), are also pests. Aquatic molluscs are controlled by a number of synthetic and botanical compounds. Terrestrial pulmonate gastropods and aquatic molluscs are collectively referred to herein as “molluscs”.
A wide variety of approaches have been used to combat pest molluscs. Perhaps the most common is the use of poisonous compounds called molluscicides. Molluscicides encompass a diverse group of chemical compounds including table salt (NaCl), calcium arsenate, copper sulfate and metaldehyde. Molluscicides, depending upon their mode of action, fall into two major groups: (1) contact poisons or (2) ingested poisons. As a contact poison, the molluscicides must come into physical contact with the exterior of the mollusc, either by external application or as a result of the mollusc traversing the bait on the ground. The poison is picked up by the proteinaceous slime coat of the mollusc and builds up in the mollusc's body until it reaches lethal proportions. One of the major drawbacks of contact-type molluscicides is that they have little effect if the molluscs are not physically touched by the chemical. Slugs or snails will be unaffected if they are hidden or migrate into an area after application of a contact molluscicide.
One of the few compounds that acts as both a contact and ingested poison is metaldehyde. This compound is commonly used as a long lasting bait, attracting the molluscs and killing them after ingestion of the compound. Despite its high effectiveness and its commercial popularity, metaldehyde is toxic to higher mammals and is a major contributor to domestic animal poisoning in the U.S. and Europe.
Heavy metals, including zinc, aluminum, copper and iron are all toxic to molluscs and are known to be effective molluscicides when used as contact poisons in the form of salts or chelates (Henderson, et al. 1990). Few of them, however, have been successful commercially, perhaps because many such compounds are not palatable to molluscs and are not ingested in sufficient quantities to be effective. Henderson et al. (UK Patent Application 2 207 866A, 1988) discovered that specific complexes of aluminum with pentanedione compounds and iron with nitroso compounds would act both as ingested and contact poisons.
U.S. Pat. No. 5,437,870 (Puritch et al) discloses an ingestible mollusc poison having a carrier (e.g., a bait), a simple iron compound and a second component. The second component can be ethylene diamine tetracetic acid (EDTA), salts of EDTA, hydroxyethlene triamine diacetic acid, (HEDTA) or salts of HEDTA. Australian Patent Application No. 77420/98 also discloses a stomach-action molluscicide that includes a metal complexone (i.e., iron EDTA) and a carrier. U.S. Pat. No. 6,352,706, discloses the composition and use of an activity promoting additive, ethylene diamine disuccinic acid (EDDS) and derivatives thereof in combination with an edible carrier.
U.S. Pat. No. 6,352,706, mentioned above, discloses that metal, especially iron molluscicidal baits, could be improved by the additive EDDS which enhanced the effectiveness of metal absorption in molluscs.
With the ingested poisons, the slug must eat and absorb the poison in large enough amounts to reach a lethal threshold. These baits are much more difficult to formulate and use than are contact poisons because the compounds are not always palatable to the slug. To be effective, these compounds must be formulated in baits that are readily eaten by the molluscs in sufficient quantities to cause a poisoning effect. If bait is too poisonous, the molluscs will cease feeding prior to absorbing enough toxins to be lethal. On the other hand, if the bait is not toxic enough the molluscs will simply eat and excrete the bait without being affected (Henderson and Parker, 1986).
It would thus be desirable to provide a molluscicidal bait composition that will enhance palatability, ingestion, digestion and residual action of stomach-action molluscicides.
WO 99/39576 describes a mollusc stomach poison composition that comprises a simple metal compound, an additive that enhances the activity and absorption of the metal, and a carrier material that is edible to molluscs. The composition is effective to combat molluscs upon being ingested by the molluscs.
According to WO 99/39576, useful salts of ethylene diamine disuccinic acid that may serve as an activity enhancing additive according to the present invention include alkali metal salts, alkali earth salts, ammonium salts and substituted ammonium salts of this compound, as well as mixtures thereof. Preferred salts include the sodium, potassium, and ammonium salts. The use of pH-adjusting additives is described in WO 99/39576, including calcium carbonate, potassium carbonate, potassium hydroxide, ascorbic acid, tartaric acid and citric acid.
Slug pellets made according WO 99/39576 are very effective but there is always a need for new and/or improved compositions.